DESCRIPTION: Dr. Zhang proposes to compare the rate of mutation in vivo during first and second strand DNA synthesis. He will utilize an in vitro assay to compare the frameshift rates of RNA polymerase II, RT first strand, and RT second strand synthesis. He will test the three prevailing models for how recombination occurs in retroviruses using in vivo and in vitro systems. He will also test the effects of RNA secondary structure on stimulation of recombination.